# All Questions

6 questions
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### Why does Bell's field theory model need to be stochastic on a space-time lattice?

In "Beables for quantum ﬁeld theory", John Bell has presented a realistic interpretation of any fermionic quantum ﬁeld theory, along the pilot-wave ideas. This model is formulated on a spatial lattice ...
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### Is there any use of a quadratic equation of state in FLRW cosmology?

Consider standard FLRW cosmology. Usually, the relation between energy density $\rho$ and pressure $p$ of a cosmological fluid component is linear: \tag{1} p = w \, \rho, \end{...
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### Systematic expansion of $e^{i\vec{k}\cdot\vec{r}}$ in atomic physics in terms of Legendre polynomials and identifying different $l$ terms

In the context of light-matter interaction one often makes the approximation $e^{i\vec{k}\cdot\vec{r}}\approx 1$. Keeping higher order terms in $e^{i\vec{k}\cdot\vec{r}}$ give magnetic dipole, ...
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### From the expansion to temperature and recovering equilibrium number densities from the scale factor

For a particle species of mass $m$, when the temperature $T$ of the Universe is $T>m$, the equilibrium number density $n$ falls as $$n\propto T^3\tag{1}$$ and for $T<m$, it falls as n\propto ...